The inventive subject matter relates to power converters and, more particularly, to multi-level power converters.
Multi-level converters are commonly used in applications such uninterruptible power supplies (e.g., for an inverter and/or rectifier), grid-tie converters, motor drive inverters, and the like. Multi-level inverters drive an output at a greater number of different voltage levels than the two output voltage levels provided by a traditional two-level inverter. Typical multi-level inverters use multiple switches (e.g., transistors and parallel-connected diodes) in series, such that each device typically sees less voltage stress in comparison to devices in a two-level converter.
There are various different circuit topologies that can be used to implement a multi-level inverter. For example, FIG. 1 illustrates a conventional 3-level “I” type multi-level converter including upper and lower switch branches including respective insulated gate bipolar transistors (IGBTs) IGBT1, IGBT2, IGBT3, IGBT4, coupled to positive and negative DC buses V+, V− and to an energy storage circuit including an inductor L and a capacitor C. Diodes D1, D2, D3, D4 are coupled across respective ones of the transistors IGBT1, IGBT2, IGBT3, IGBT4. Neutral clamping diodes D5 and D6 couple respective ones of intermediate nodes N1, N2 to a neutral N. Capacitors C1 and C2 are coupled between respective ones of the DC buses V+, V− and the neutral N. FIG. 2 illustrates a conventional 5-level I-type multi-level converter including upper switch branches including transistors IGBT1, IGBT2, IGBT3 IGBT4 and parallel-connected diodes D1, D2, D3, D4, lower switch branches including transistors IGBT5, IGBT6, IGBT7, IGBT8 and parallel-connected diodes D5, D6, D7, D8, clamping diodes D9, D10, D11, D12, D13, D14 and capacitors C1, C2, C3, C4. FIG. 3 illustrates a conventional “T” type multi-level converter, including upper and lower switch branches including transistors IGBT1, IGBT4 and parallel-connected diodes, a neutral clamping switch branch including transistors IGBT2, IGBT3 and parallel-connected diodes D3, D4, and capacitors C1, C2.